Illumination systems are used in many different applications, including projection display systems, backlights for liquid crystal displays and the like. Often, projection systems use one or more white light sources, such as high pressure mercury lamps. However, increasingly, light emitting diodes (LEDs) have been considered as alternatives to other white light sources. LEDs have the potential to provide the brightness and operational lifetime that would compete with conventional light sources. Current LEDs, however, especially green emitting LEDs, are relatively inefficient.
Because of this inefficiency, wavelength converted light emitting diodes (LEDs) are becoming increasingly important for illumination applications where there is a need for light of a color that is not normally generated by an LED, or where a single LED may be used in the production of light having a spectrum normally produced by a number of different LEDs together.
One approach to generating white light with a single LED is to first generate blue light with the LED and then to convert some or all of the blue light to a different color or colors. For example, a portion of the blue light may be converted to red light, and a portion of the blue light may be converted to green light, such that the resultant output light, when mixed, is white. The light correcting process can result in recombination of free carriers at the surface of the converting layer. Such recombination can lead to degradation of the semiconductor and reliability issues. It would therefore be desirable to have a wavelength converted light emitting diode (LED) that addresses these surface recombination issues to provide for more reliable and improved performance.